The objective of this series of experiments is to behaviorally and physiologically evaluate the equilibrium readjustment which occurs as a function of time after the selective lesion placement in different portions of the body equilibrium system. Locomotor imbalance, postural asymmetry and oculomotor abnormality are examined simultaneously in quantitative and repeated manner in squirrel monkeys. For the analysis of lateral deviations during locomotion, the squirrel monkey platform runway test, which is a lateral deviation measure in a natural trot, is used. Moreover, the EMG recordings from bilateral gastrocnemius (and tibialis anterior) muscles and step recordings from each foot are analyzed in rotating-cage running monkeys to evaluate the vestibulo-fugal effects appearing in the hind leg muscle activities. For the evaluation of static body balance function the squirrel monkey statokinesimetry is developed in conjunction with the grip force measurements and EMG recordings during their natural (perching) posture maintenance. Experimental lesion placements confirms the importance of each individual portion of the body equilibrium system. Lesions include both peripheral and central lesions, and also combined lesions, and will be confirmed microscopically. Another purpose of this experimental series is to evaluate importance of other modality input such as visual or proprioceptive inputs toward the vestibulogenic disequilibrium compensation.